Fertilized eggs must "activate" for development to begin. For example, activation is needed to block polyspermy, resume meiosis and start embryo mitosis. Although activation is critical for fertility, little is known about its control apart from a key role for calcium. The powerful genetics of Drosophila permits efficient discovery of new regulators of activation and detailed dissection of the pathways through which they act. The first Aim investigates the regulatory cascades that control activation. Our in vitro and genetic data show that calcium, via at least one conserved signaling pathway, mediates activation in Drosophila. We will test whether two other important transducers of calcium signals are also required for activation. To "flesh out" the pathways that regulate activation, we will determine the molecular identity of two new genes whose mutants fail to activate. We will explore how these and other molecularly-identified genes interact with each other, and with calcium signaling, to cause activation. We will follow up our findings that the activity of MAPK, a major signaling kinase, drops during activation, and that activation makes the egg cytoplasm competent to organize the male pronucleus. The second Aim focuses on events set in motion by activation. We investigate YA, one of the few proteins known to act in these events. YA associate with chromatin and with the nuclear lamina, to permit mitosis by coordinating the cell cycles of the pronuclei. We will determine whether YA acts only immediately after activation. We will identify histone- and chromatin- protein modifications in pronuclei entering mitosis, and YA's effect on these modifications. We will identify the nature and actions of YA's nuclear partners. YA is dephosphorylated upon egg activation, and as a result enters nuclei. This strongly suggests that activation causes changes in protein phosphorylation and activity. We will test this hypothesis by determining how activation changes the phosphorylation state of the proteome. We will identify the functions of selected proteins whose phosphorylation state is regulated by activation. RELEVANCE: "Activating" a fertilized egg to begin development is essential for fertility. Knowing the molecules and functions that control egg activation is important for diagnosing early infertilities and improving the efficiency of assisted reproductive technologies. We found that the control of egg activation is similar in Drosophila fruit flies and mammals. Thus, we exploit the powerful genetics of Drosophila to elucidate efficiently the molecules and gene pathways needed to start development in humans.